It has been proposed, as in my U.S. Pat. No. 3,026,665 and in my co-pending application Ser. No. 581,029, filed May 27, 1975, now U.S. Pat. No. 4,035,994 to connect a rotary lawn mower blade to its driving engine through a centrifugal clutch having centrifugal shoes on the clutch driver which are normally retracted at engine idling speeds and which at engine operating speeds are centrifugally engaged with a driven clutch drum fixed to the rotary cutting blade. A blade brake, such as a band engaging the external surface of the clutch drum, normally holds the blade stopped under engine idling conditions. When the operator actuates a deadman control, this concurrently releases the brake and opens the engine throttle. The resulting higher engine speed actuates the centrifugal clutch so as to drive the drum and the blade. The primary purpose of this blade control arrangement is safety, so that the blade will not be driven except when the operator of the lawn mower is in a proper operating position and appropriately holds the deadman control handle in actuated position.
I find that an usafe condition can occur with this arrangement when the engine stops, as from running out of fuel or because of some other failure, while the deadman control is held in its actuated position. Under these conditions, the engine stops and the centrifugal clutch disengages, but since the brake is held disengaged by the actuated deadman lever, the blade and the driven clutch drum are free to rotate from the momentum of the blade. Such rotation makes no noise, and since the engine is stopped and silent, the operator may assume that the blade is stopped when in fact it may be rotating at considerable speed and with considerable momentum.
The present invention provides a warning device which operates under these conditions, namely, when the engine is stopped and the clutch disengaged but the brake is also disengaged so that the blade and driven clutch drum are free to rotate from their own momentum.